Our objective is to provide detailed structural information, through systematic crystallographic investigations, necessary in understanding the structure-function relationship of the glutathione S-transferase provide protection against cancer-causing genotoxic electrophiles. GST is also found to be closely related to the lifespan and aging of the female mouse, where a reduced GST level was implicated to be related to increased susceptibility to disease and drugs occurring with advance age. It has also been suggested that GSTs play a pivotal function in the immuno defense against parasites. Vaccinations of rats, mice and baboons with S. Mansoni GST have resulted in a significant reduction of the worm populations. In recent years it has also been suggested that GST is responsible for drug resistance in some tumore cells. Thus a knowledge of the structure-function relationship of this family of enzymes may have long-term significance in understanding problems related to prevention of cancer, control of tumors, treatment of parasitic diseases, and understanding of stress in the aging process. We have recently grown a mu-class GST into four different crystal forms and have obtained crystals for four humanalpha-class GSTs, making a total of eight crystal forms. W have now solved the structures of five of these crystal forms by molecular replacement methods. In this proposal we plan to refine these crystal structures. We aim to compare their structures in order to identify the conformational changes due to the substrate binding. We aim to locate the binding site for the electrophilic substrates,its location is unknown at the present. We plan to compare the structures among different classes of GSTs. In addition, we plan to crystallize and to solve the structures of Drosophila GSTs, one of which has sequence homology to the stringent starvation protein of E. coli. We also plan to crystallize and study the mutant structures of GSTs. The proposed research could answer many of the key questions about the structure- function of GST. It will also increase our knowledge concerning the molecular basis of macromolecular recognition in general.